Clearing blocked condensate drain pipe for AC unit

I have a York split air conditioning unit in my basement. The unit was fitted with a condensate drain made from 3/4" poly butyl (PB) piping (as used for the water supply in the rest of the house) with crimped copper fittings. The pipe runs on a slope from the condensate outlet around 10' (with two 90 degree turns) and then disappears (with another 90) down through the slab, presumably connecting to a main floor drain underneath. The pipe appears to be partially clogged somewhere in the line and backs up when the cooling unit is working hard - need I say more - leaked water all over the basement floor, and have now got a tub under the open outlet to catch the outflow while I find a solution.

I'm thinking to replace the length of (above floor) pipe and include a trap in the line so as to avoid this problem in the future. I'll probably use some CPVC pipe and fittings that I kept from another project. The immediate concern however is unclogging the line and before cutting any pipe I'd like to see if can clear the line by other means. I've tried poking some wire down to the first turn with no success. Attempting to flush out the line with a garden hose I can imagine would be a mess.

'oxy-bleach' (percabonate) cleaner, is supposed to be 'safer' than clorox and strong acid/alkali based 'openers'. Anyone know if it's OK to use with PB pipe or can recommend something suitable?

Other thing is, since I don't have any crimping materials, can PB pipe be glued to CPVC fittings, with CPVC glue that is? Or else if I remove the PB pipe at one of crimped copper fittings, what would be the best fitting (?compression) to connect 3/4" CPVC pipe to the copper fitting, bearing in mind that it is just for drainage and not under pressure. Might pay to have something that can be undone for maintenance in the future.

Wanting to use leftover pipe and fittings is commendable, but not a wise choice of material. The inside diameter of CPVC is something like a size smaller than other media such as PVC or copper. You are not draining potable water, so PVC would be a good and cheap alternative. I'm not familiar enough with the PB pipe to advice on exactly how to connect the PVC to it, but a neoprene sleeve with clamps on both ends would be one way assuming you can find the sleeve in the proper size. There may be some kind of adapter or combination of fittings that would work as well. Remember, there is no pressure in this line, so there would be no problem there. You need to understand that CPVC and PVC "glue" is not really glue at all. They are solvents that briefly liquify the top surfaces of pipes and fittings so when the pieces are joined the two surfaces blend together and form a chemical weld. Quite similar to metal welding. I can't give you specific information on oxy-bleach (is this Oxy-Clean?) but chemical drain cleaners of any kind are not effective on clogged drains in spite of what TV commercials would have us believe. You might try connecting a hose to the pipe and using water pressure to push the clog out.

Wanting to use leftover pipe and fittings is commendable, but not a wise choice of material. The inside diameter of CPVC is something like a size smaller than other media such as PVC or copper. You are not draining potable water, so PVC would be a good and cheap alternative.

I'm not familiar enough with the PB pipe to advice on exactly how to connect the PVC to it, but a neoprene sleeve with clamps on both ends would be one way assuming you can find the sleeve in the proper size. There may be some kind of adapter or combination of fittings that would work as well. Remember, there is no pressure in this line, so there would be no problem there.

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I'll see what I can find. Like you say, it's not under pressure, so a sleeve plus worm-clips might suffice, for now at least.

You need to understand that CPVC and PVC "glue" is not really glue at all. They are solvents that briefly liquify the top surfaces of pipes and fittings so when the pieces are joined the two surfaces blend together and form a chemical weld.

I can't give you specific information on oxy-bleach (is this Oxy-Clean?) but chemical drain cleaners of any kind are not effective on clogged drains in spite of what TV commercials would have us believe.

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Oxy-Clean is one of the brands (Arm & Hammer). Seems there is an eco-friendly oxygen-bleach (peroxide) alternative for every traditional chlorine based product now. I can attest that the stain remover powders (containing just sodium percarbonate/sodium carbonate) are marvelous for cleaning wood decks, vinyl sidings etc, but I likewise have no experience using this type of product for unblocking drains. Probably depends a lot on what the nature of the blockage is.

You might try connecting a hose to the pipe and using water pressure to push the clog out.

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If I find a suitable connector, I'll maybe cut the pipe just above where it goes down through the slab take it outside and put a hose through it. If it clears a clog, all well and good, and I'll patch the pipe back on, for now. But if it's blocked further down the line, I'll have to rethink. Unfortunately, the section going through the slab is pretty much encased, but at least I'd have a more distance from the furnace to attach a hose without worrying that it's going to blast water over the furnace and electrics.

Cut the pipe and hosed it all out. Rejoined the pipes with a plastic 3/4" shark-bite union ($4). Seems to be OK and the condensate is now draining. Looking at the plugs of gelatinatious gunk that came out, I reckon it would probably have cleared with the oxy-bleach, but it's done now.

I'll replace the section with PVC pipe to include a trap and re-using the union with a fresh metal 'bite', but the problem is solved for now.

I'm pretty sure the blockage had built up over a section of the PB pipe where it had sagged, so hopefully replacing with PVC pipe and better support should avoid/minimize that. With addition of a p-trap, I'll need to put in a couple of unions anyway. The pipe runs across the slot where the fan filter goes in. Until now I (and presumably the previous owner) have had to pull the pipe out of the condensate outlet and bend it down in order to replace the filter; probably one reason why the pipe had sagged over the years. Putting unions either side of the filter slot will allow me to remove that section of the line when I need to change the filter; a bit tedious but there's no other way round.

Crikey, reading about p-traps I'm really surprised that one was not put in when the heat pump was installed more 10 years ago. It's a classic negative pressure configuration with the furnace/blower above the cooling unit. Strange thing is, in the 3 years I've been here, this is the first summer I've encountered such a leak, but I can see what's happened now.

Partial clog builds up. Pipe does drain slowly, but the negative pressure retains the condensate in the unit while the blower is running. When the blower goes off, there is an outflow of built up condensate that the partially blocked drain cant handle and the water backs up. I see water spilling out of the pipe connection to the outlet and assume that it's just because the connection is loose and leaking. So I bind it with teflon tape to get a better seal, but as a result the water backs up into the unit itself, overflows and starts leaking out from underneath. Not a good situation.

Definitely need a p-trap and a schedule for periodic clean-out of the drain line.

On the subject of condensate p-traps I came across this article that explains why the trap design and dimensions are so important in determining whether the trap will actually work or fail, especially for negative pressure configurations:

Page 7 gives the appropriate dimensions, which in turn requires knowledge of the negative pressure (vacuum head) in inches Hg that system is pulling when the blower is running.

I'm sure HVAC technicians carry such things, but can anyone recommend a suitable pressure gauge (or simple manometer) and who might stock them in the Montreal area (Home Depot, Rona, Reno Depot?). Otherwise, I guess one could play around with piece of flexible plastic tubing to determine the optimum configuration that allows flow of condensate while the blower is running.

Well, I decided to go ahead and make a test p-trap from 3/4 PVC pipe connected with four 45 degree elbows to get the loop. Used a nominal value of 1 inch negative pressure, giving a drop of about 4" on the inlet side of the loop. I then just kept shortening the outlet side of the loop until I got a steady trickle of condensate with the cooler and fan running, all of the time checking with a lighter flame that there was no air pull back up the trap. I'll leave it unglued for now too see how it goes. If I find that it snags crud and blocks too easily I might try heat bending some pipe to the same dimensions.

I can't give you specific information on oxy-bleach (is this Oxy-Clean?) but chemical drain cleaners of any kind are not effective on clogged drains in spite of what TV commercials would have us believe.

There is no way I would attempt to read the voluminous texts above, so I do not know if anyone addressed the real issue here. IF the condensate is connected to the drain line, anywhere except above an "active" trap, the unit is going to "inhale" sewer gas odors and disperse them through the building. The trap on the condensate line ONLY works during high humidity periods. The rest of the time it dries out and sucks air in through the drain line.